MENAI SUSPENSION BRIDGE (FROM ACORRESPONDENT)
Menai Strait from Anglesey Column
“This stupendous structure was opened for general intercourse on Monday, the 30th of .January, at half past one in the morning. As the season was considered unfavourable for a public celebration1 the Commissioners determined that the opening should be quite private; and, in pursuance of this resolution, a meeting was held the previous evening at Bangor Ferry, to make the final arrangements. Mr. W. A. Provis, the Resident Engineer was then dispatched to meet the London down mail, and take charge of it across the Bridge. Having mounted the box with David Hughes the coachman, and Reid the guard, the Mail proceeded, and on its way to the bridge took up Mr. Akers, the Mail Coach Superintendant, Mr. Hazeldine, the contractor for the ironwork, Mr. J. Provis, the superintendant for proving and examining it, Mr. Rhodes, who has had charge of erecting the iron and timber work, Messrs. W. and J. Wilson, sons of the contractor for masonary, Mr. Esplen, an overseer, and as many more as could be crammed in, or find a place to hang by. Thus loaded, amidst the blaze of lamps, the cheers of those assembled, and the roaring of a heavy gale of wind, the dates were thrown open, and the Mail passed triumphantly across.
About 9 o’clock, that excellent and indefatigable Commissioner Sir Henry Parnell, and the Chief Engineer, Mr Telford (whose works are his best Eulogium) passed over in the carriage of the latter. Throughout the remainder of the day, the number of carriages, horses1 and persons which passed over was immense; the bridge was literally crowded, and tickets could not be issued fast enough for the demand. The evening was spent by the workmen with much fun and feasting, and the sons of the Sister Kingdoms seemed to have but one feeling, in wishing “Success to the Bridge”, and promoting the general hilarity.”
Menai Strait Bridges
For centuries, travel to Anglesey from the mainland was often hazardous. Ferries traversed the Menai Strait at various places, but the currents are tricky and numerous boats capsized or ran aground, often with loss of life.
One of the most tragic occurred in 1785 when a boat carrying 55 people became stranded on a sandbar in the middle of the southern end of the strait. Attempts to refloat the boat left it swamped. The alarm was raised and rescuers set off from Caernarfon. But, the combination of high winds, nightfall and the fear of also running aground meant that the rescuers could not approach the sandbar. Night fell, the tide rose and those stranded on the sandbar were swept away. Only one survived.
Menai Bridge
White Knight says to Alice,‘I heard him then, for I had just completed my design.To keep the Menal Bridge from rust.By boiling it in wine.’
Lewis Carrol, Through the Looking Glass
Menai Bridge
Traffic across the strait and Anglesey increased in the early 19th century after the Act of Union of 1800, when Ireland joined the United Kingdom. Travellers to the ferry port of Holyhead, where ships left for Ireland, had to make the dangerous crossing after a long and arduous journey from London. Soon plans were drawn up by Thomas Telford for ambitious improvements to the route from London to Holyhead, including a bridge over the Menai.
One of the design requirements for the bridge was that it needed to have 100 feet of clear space under the main span, to allow for the passage of the tall sailing ships that plied the strait. This was done by designing a suspension bridge, with sixteen massive chains holding up a 579 foot length of road surface between the two towers. Although small suspension bridges had been built before, none approached the scale that Telford proposed for this one.
Despite much opposition from the ferry owners and tradesmen in the ports, construction of the bridge started in 1819. The stone used for the arches and piers was limestone quarried from Penmon Quarries at the north end of the strait, then carried down by boat. The ironwork came from Hazeldean’s foundry near Shrewsbury. To prevent the iron from rusting between production and use on the bridge, the iron was immersed, not in boiling wine as the White Knight suggested above, but in warm linseed oil.
The stonework was finished in 1824; then began the monumental task of raising the chains that would hold up the central span. Tunnels were driven into solid rock on either shore to anchor the chains. Then the first section of the chain was secured oil the Caernarvonshire side, drawn up to the top of the eastern tower and left to hang down to the water level. Another chain was drawn up to the top of the tower on the Anglesey side. The central section of chain, weighing 23.5 tons, was then loaded onto a raft, carefully manoeuvred into position between the towers and connected to the dangling chain. While a fife and drum band played to encourage the workers, 150 men used block and tackle to draw the chain up to the top of the Anglesey tower to complete the span. The large crowd that had gathered to watch cheered wildly as the connection was made.
The remaining fifteen chains were raised in a similar manner over the next ten weeks. Rods were then hung from the chains and bolted to iron bars that were used as the base for the wooden road surface. The bridge was opened on 30 January 1826 to great fanfare. Its completion, along with other improvements to the road by Telford, reduced travel time from London to Holyhead from 36 hours to 27 (today it takes 5.5 hours).
The bridge has been modified and reconstructed many times over the years. The road surface was damaged in severe winds in 1839 and needed repair. The wooden deck was replaced with a steel one in 1893. With the coming of modern vehicles the previous weight limit of 4.5 tons per vehicle became an impediment. Overweight vehicles would have to carry their loads over in two or more trips. In fact, even bus conductors would regularly have to ask some passengers to walk across. So, between 1938 and 1940 the old iron chains were replaced with new steel ones, all while traffic continued to cross. In the autumn of 1999 the bridge was closed for several weeks to completely replace the road surface and strengthen the bridge.
Britannia Bridge
Britannia Bridge from Church Island
The completion of the Menai Bridge was a boon in easing the journey to the island, particularly for travel to Ireland. However, the rapid rise of rail travel later in the 19th century meant that there was soon a need for trains to cross the Strait. When plans were first being made to build a railway to Holyhead it was proposed that the carriages be taken over the Menai Bridge; the carriages would be uncoupled from the locomotive at one end, then drawn across one by one, using horses, to a waiting locomotive at the other end.
This idea was abandoned and plans were drawn up for a new bridge by Robert Stephenson, son of the locomotive pioneer George Stephenson. He faced the challenge of building a bridge rigid and strong enough to carry a heavy train of many carriages. This was done by making the bridge out of two long iron tubes, rectangular in shape, through which the trains would travel.
When first conceived, the tubular bridge was to have been suspended from cables strung through the openings at the tops of the towers. However, after engineering calculations and tests of the finished tubes it was decided that they were strong enough by themselves to carry the trains.
Like the Menai Bridge, the stonework of the Britannia Bridge was constructed of limestone from Penmon, although sandstone from various places was used internally. The tubes themselves were constructed on the banks of the Strait.
Stephenson faced a much greater challenge in raising the 1,500 ton finished tubes than had Telford with his much lighter chains. He too would float the tube into position. However, the process didn’t go as smoothly with the first tube as with the Menai Bridge chains and the giant tube came close to being swept out to sea. Fortune prevailed and it did finally end up in place. Then, very slowly, using hydraulic f5umps, the tube was raised into position. Stonework was built up under the ends of the tube as it was lifted; this was to support it if the lifting equipment failed. This was fortunate because one pump did indeed fail, but the tube only fell nine inches.
Menai BridgeWith the tubes in place the final touches were added. These are the four magnificent limestone lions that guard the entrances to the bridge. They were carved by John Thomas, who had also done stone carving for the Houses of Parliament and Buckingharn Palace in London. The lions are almost 4 metres high and sit on plinths of equal height. The bridge was opened on 5 March 1850.
The present day bridge has a much different appearance than the original. This is because it has been reconstructed after a disastrous fire in 1970. A group of teenagers looking for bats in the dark tubes accidentally dropped the burning paper they were using as a torch. This eventually started a ferocious fire through the whole tubular structure that caused so much damage to the tubes that they were in danger of falling into the strait.
As assessments were being made as to how to repair the bridge the local County Surveyor came up with the clever idea of making two bridges out of one. For many years there had been discussions of building a third bridge~
Britannia Bridge across the strait to ease the traffic coiThestion after reconstruction on the Menai Bridge. It was proposed that theBritannia Bridge be rebuilt as a two level bridge carrying both trains and road traffic.
Rather than being a tubular bridge the new span is now supported by arches. A single railway track carries the trains to and from Holyhead. On top of this is a roadway carrying traffic on the A55 Expressway. The traffic on the bridge is monitored by a video camera that is now connected to theInternet.
And today, the lions that once had pride of place at the entrance to the tubular bridge now sit forlornly below the road surface as thousands of vehicles thunder past.
Update – The closure of the Menai Bridgefor repairs in 1999 caused severe traffic problems on the Britannia Bridge. This, plus the increase in traffic that inevitably will be caused by the building of a new dual-carriageway across Anglesey, means that there have been new calls locally for a third crossing to be built across the Strait. One favourite option is to build a new deck on top of the Britannia Bridge, so that it has two levels for cars. Whether this will happen remains to be seen.
Update 2, Oct. 2001 – The latest DIan being discussed to ease traffic is to build a tunnel underneath the strait, with one entrance near Gaerwen and the other beyond Bangor. It has been estimated that this would cost at least as much as the whole dual carriageway across Anglesey. It also m~y not be feasible because the strait is formed from a geological faui’rwhich is still occasionally active. An alternative is to convert the Britannia Bridge from two to three lanes, with the traffic direction of the centre lane changing at different times of the day.
Travelling from England to Ireland
At the commencement of the eighteenth century a voyage from England to Ireland was not lightly undertaken. The vile condition of the Welsh roads compelled travellers to make either Bristol or Liverpool the port from which to sail. The ships of those days were far from being commodious or comfortable, and when, as often happened, contrary winds and storms protracted the voyage, the passengers fared badly.
Now, the map shows very clearly that Holyhead, at the northwest corner of the island of Anglesey, is much nearer the Irish coast thanis either Liverpool or Bristol, and this geographical fact presently made it the fashion to brave the joltingsof Welsh mountain tracks in preference to the tossings of seventy miles of Irish Sea. It is true that the Holyhead route included the crossing of the Menai Straits, which, in certain states of tide and weather, was a very unpleasant business; and when these had been negotiated, there remained theroads of Anglesey, which were, if possible, worse than those ofWales. To the credit side of the Holyhead route could be placed thefact that Anglesey and Liverpool were equidistant from many of thelarge midland and southern towns.
Telford’s Road to Holyhead
In 1810 the great engineer, Mr. Thomas Telford, was engaged to deal with the roads between Shrewsbury and Holyhead, via Llangollen, Bettws-y-Coed, and Bangor. He blasted rocks, built parapets, and formed embankments, until, in the place of rough, steep mountain tracks and tenacious quagmires, there was a wide, safe, and splendidly graded road, which even at this day is one of the best in the British Isles.
He decides to bridge the Menal Straits
But there still existed the irksome passage of the straits. Until these were bridged the road would be incomplete. Mr. Telford under took to span the gap. He submitted two plans for arched bridges, one of which showed a 500-foot cast-iron arch, to be supported during construction on centres suspended from large frames rising on the two shores. Both these plans were ruled out, however, on the ground that they would interfere seriously with the navigation of the straits; so the engineer decided on a suspension bridge which should clear the water by 100 feet or more-sufficient to permit the passage of a tall ship. The site chosen was at a point where the shore on either side rises steeply, and where the straits are about 800 feet wide at high tide. The distance between abutments is just short of one-third of a mile. To span this, Telford specified two short embankments, 7 arches of 52 1/2 feet span, and a main suspension span over the channel of 550 feet between the centres of the towers.The last factor taxed Mr. Telford’s ingenuity severely. Such a span was at the time unprecedented, and the safe accomplishment of the task demanded that a vast amount of preliminary experiment should be devoted to the huge chains forming the distinguishing feature of the structure.
The Building of the Piers.
An Act empowering the building of the bridge was passed in 1819, and Telford lost no time in getting to work. The foundations of the two main piers, each 153 feet high, were taken in hand first, and while the piers rose the arches of the two approaches rose with them, the chief difficulty being that of providing sufficient stone to keep the army of masons engaged. As the piers would be subjected to the Piers severe lateral strains, their individual stones were bound together by iron clamps, in much the same manner as the components of a lighthouse. Four large cast-iron saddles, running on rollers, to carry the suspension chains, capped each pier. Their easy movements over the rollers provided for the expansion or contraction of the chains as the temperature of the air should vary.
Anchoring the Suspension Chains.
Since the efficiency of a chain depends ultimately on secure attachment, every care was taken to ensure firm anchorages for the chains of this bridge. The method adopted was to drive four parallel tunnels obliquely down into the native rock for a distance of 20 yards or more, and excavate a chamber across their lower ends. In this chamber were built up massive transverse anchorage frames, resting against the walls of rock separating the tunnels, and therefore immovable unless the rock itself were torn away – a contingency that was practically negligible.
The chains, sixteen in number, were composed of 1/2 inch bars of iron. Thirty-six bars – corresponding to the strands of a wire cable -were grouped together to make a square chain four inches on the side, the components of the chain being wrapped with iron wire. The weight of the portion of the chain between the two suspension piers was over 23 tons; its length, 570 feet.
An Experiment.
The masonry completed, preparations were made for hoisting the chains into position-a process to which Mr. Telford looked forward with the greatest anxiety. In order to obtain exact figures as to thepower required to hoist a chain and give it the correct curvature between the piers, he fastened together, end to end, a number of iron bars totalling five hundred and seventy feet in length. These were laid out in an adjacent valley, and raised at the ends until the centre was clear of the ground and the curve was the same as that of the suspension chains to be. From the stresses recorded, Telford calculated that a pull of thirty-nine and a half tons would be needed to handle the central span of a chain.
Each chain was divided into three parts – two to reach from the anchorages to the piers, the third to span the channel. One of the land sections – that on the Carnarvon side – was long enough to extend down the seaward side of this pier to water-level; the other reached only to the pier saddle. The rest of the chain was built on a raft 450 feet long and 6 feet wide, ready to be floated to a position between the two piers.
Hoisting the Chains.
On April 14, 1828, the hoisting of the first of the chains took place under the eyes of thousands of people who gathered from far and near to witness the subjection of the straits. In the afternoon, shortly before high water, the raft bearing the chain was taken in tow by four boats, swung round, and moored across the straits on the line of the bridge. One end was then made fast to a loose end of the Carnarvon section, and to the other were attached strong ropes leading over the top of the Anglesey pier to two capstans on the shore. At the given signal 150 sturdy labourers threw their weight on the capstan bars. Slowly the chain rose from the raft, and yet more slowly, as less and less weight was water-borne. Presently a great shout arose when the raft, now entirely freed from its load, floated down the tide.
The Junction made.
For another hour the crowd watched the curve of the made chain grow flatter and flatter, and the word went round that a junction had been made with the Anglesey land section – in fact, that a continuous chain now extended from Anglesey to Wales. This provoked a fresh outburst of cheering, which in turn encouraged some foolhardy workmen to use the chain as an unlicensed bridge and win the perilous honour of being the first to cross the straits by an aerial pathway.A Foolhardy Feat.
Not that they were so daring as a workman on the great cantilever bridge across the Niagara gorge, who, when but a narrow gap separated the two cantilever arms, laid a plank across it, walked deliberately to the middle, and stood on his head, kicking his legs about just to show how little he cared for the whirlpool raging two hundred feet below
The Bridge opened.
The remaining fifteen chains were raised in the same manner as the first, and by July 9, 1825, the last was in place. A band ascended to a temporary platform on the centre of the span and played the National Anthem to the crowds which had assembled for the occasion. Then followed the more prosaic work of attaching the roadway of stout planks to the vertical suspension bars of inch-square iron. By the end of the year the structure was complete, and on January 30, 1826, a stage-coach made the passage of the bridge at the head of a great procession of people of all ranks.
Menai SusDension Bridge from the Canarvon side. Menai Susr~ension Bridge from the Anglesey side.
Facts and Figures.
This remarkable bridge has a roadway length of just 1,000 feet, while the suspension chains measure 1,715 feet from anchorage to anchorage. The roadway, 30 feet wide, gives accommodation for two carriage-ways and a footpath. Over 33,000 pieces of iron, weighing 2,187 tons, are incorporated in the structure, the cost of which was £120,000. During a gale the bridge oscillates slightly, but the crossing of heavy vehicles does not affect it sensibly.
The Conway Suspension Bridge.
Simultaneously with this bridge Telford erected~one of similar construction across the mouth of the Conway River, to benefit travellers on the Chester-Holyhead road, by abolishing the need for ferrying across the river. The Conway Bridge, which has a central span of 327 feet and a width of 32 feet, was also opened for traffic in 1826.Though now more than eighty years old, both these bridges are, to all appearance, “as good as new,” and there is no reason to doubt that for many years to come they will stand as a memorial to the engineer who greatly dared and successfully accomplished.
Tubular structure of the Britannia BridgeTHE BRITANNIA BRIDGE
The Chester Holyhead Railway
In countries of old civilization first comes the road, then the railway. The twelve years that followed the completion of Telford’s suspension bridges were remarkable for the development of the steam railway. By 1838 George Stephenson was surveying with chain and level the line of the Chester-Bangor road along the north coast of Wales, with a view to constructing a railway to Holyhead. For the crossing of the Conway estuary of the Menai Straits the bridges then existing could, so Stephenson maintained, be used for trains, though he considered that it would be advisable to relieve the Menai Bridge by moving trains over it by living horse power, as the concentrated weight of a locomotive might be expected to cause serious undulations of the roadway.
A Bridge required for the Menai Straits
When Robert Steihenson took over the construction of the railway from his father, it was decided that special bridges for trains should be thrown across the Conway and the Menai Straits, and he was asked to draw out designs. The site selected by him was about a mile south of the suspension bridge, where the waterway is some 900 feet across at high tide, and where a rock, named the Britannia Rock, rising in mid-channel, offered a convenient base for a central pier.
An Arch Bridge projected but disallowed
Like Telford, Stephenson first designed an arch bridge, his having two main spans of 450 feet each; and, like Telford, he incurred the displeasure of the Admiralty, who demanded a bridge which should give a clear headway of 100 feet right across the channel, not at certain points only. Furthermore, My Lords forbade the obstruction of the waterway while the bridge, of whatever type it should be, was in course of construction. The arch principle having been ruled out, and the suspension principle being unsuitable, Stephenson’s choice was narrowed down to a stiff truss of some kind.
Plans for a Tubular Bridge
It occurred to him that huge iron tubes, large enough for trains to run through them, might be made of sufficient stiffness to span a gap of 450 feet or more. The most efficient form, and the disposition of metal in the tube, were made the subject of exhaustive experiments, in which Mr. William Fairbairn took an important part. Model tubes of one-sixth full size were constructed and tested, and from the results so obtained was established the superiority of rectangular tubes, specially strengthened at the top, over tubes of circular or elliptical section.
Chief Features
The following was the general scheme of the bridge, for the erection of which parliamentary powers were sought. On the Britannia Rook, and on the shores of the straits, at about high-water mark, would be built three huge piers of masonry, having openings 100 feet above high-tide level (for the tubes). The four tubes of the two main spans were to be 460 feet long, 15 feet wide, and 30 feet high at the Britannia Tower, whence they tapered slightly vertically towards the shore. For the two land spans, four tubes, 230 feet long each, would be needed. All eight tubes were to be built up of riveted boiler plates, ranging from 2 inch to 7 inch in thickness, supported internally by strong ribs of angle iron, and strengthened at the corners, to prevent distortion, by triangular gussets. The roof of a tube was composed of eight flues, 21 inches deep and 20 inches wide, as experiment had shown that a group of flues gave, for a fixed weight of metal, greater strength to the top member than could be obtained from plates assembled in the same way as those of the sides.
Huge Tubes
Stephenson decided to build the short land tubes in their final positions on “falsework” of stout timbers, and, as the Admiralty conditions prohibited this system for the main spans, to take a leaf out of Telford’s book and construct the tubes for the latter on platforms on the Carnarvon shore, float them between the piers, and raise them to their final elevation by means of hydraulic presses.
A Busy Scene
As soon as Stephenson’s plans had received official sanction, preparations were begun for pushing the work ahead vigorously. Fifteen hundred workmen were collected, and soon the shores of the straits echoed with the blows of mallets and hammers. When the wharves, workshops, and other temporary structures had been built, large gangs of masons attacked the Britannia Rock and the sites of the two land towers and abutments, while labourers, aided by many horses and carts, heaped up the approach embankments of the bridge. Ship after ship came to anchor in the straits with its load of timber for the scaffoldings or of stone for the masonry.
Material needed for the Towers
The building of the towers and abutments was in itself a great work. The 230-foot Britannia Tower alone consumed 150,000 cubic feet of Anglesey marble and as many feet of limestone; and even greater quantities were needed for the two land towers, each 160 feet high. To render the elevation of the large tubes possible, vertical openings were left in the masonry of all three towers, in which the ends of the tubes would move upwards to their berths like the frame of a window in its sash.
Riveters and Rivets
While the towers and land spans were in progress, gangs of riveters working on the shore platforms joined up the plates and other members of the main spans. No fewer than two million rivets, each four inches long and seven-eighths of an inch in diameter, and totalling and nine hundred tons in weight, were used to hold the tube plates together.
Preparations for floating the First Tube
When the first of the tubes approached completion, a portion of the wooden platform under each of its ends was removed, and the rock beneath excavated to form a dock large enough to accommodate four pontoons, each 98 feet long, 25 feet wide, and 11 feet deep. All eight pontoons were furnished with large valves, through which the water passed in and out as the tides rose or ebbed. The combined buoyancy of the pontoons – 3,200 – tons exceeded the weight of the tube and its apparatus by about 1,400 tons.
The Hydraulic Presses
By the middle of June 1849 tube No. 1 was ready for moving. In the upper part of each of the towers for which it was destined had been placed iron beams, 40 feet above the rectangular tube openings, to support a hydraulic press of 2,620 tons lifting power. Each of the two cylinders of a press was 9 1/2 feet long, nearly 5 feet in diameter, and weighed 16 tons. Its piston had a diameter of 20 inches and a stroke of 6 feet, and moved in a vertical direction. To its upper end was attached a crossbeam, from which depended two chains, composed of series of eight or nine flat plates bolted firmly together. The links were 6 feet long, and “stepped” near the eyes, so that when the press had made its full stroke the chain could be gripped by a huge clamp, and sustained while the piston was withdrawn for the next lift and given a fresh grip in the chain. Each chain was 145 feet long and weighed 25 tons.
The floating of a tube to the bottom of the towers was no easy matter, owing to the strength of the current running through the straits. Elaborate precautions, including the provision of guide-ropesand capstans, were taken for controlling the pontoons and their freight, and swinging them gradually across the channel as they neared the towers.
The Tube afloat
On the evening of June 19 a huge crowd began to gather from far and near. Spectators knew that they would behold such a sight as most of them were never likely to see again. As the tide came in, the pontoons, of which the valves had been closed, lifted slowly, shouldering their mighty load. Presently the shout arose, “She floats !“ But a slight accident prevented operations being continued till the following evening, when the pontoons swung out into the channel, one end of the tube describing part of a circle. Guided by its hawsers, this strange craft moved slowly down towards the bases of the towers, in which recesses had been prepared for the tube.
A Mishap and a Rescue
As it got broadside on to the current the pull on one of the controlling capstans became so violent as to drag the mechanism bodily from its foundations. For a few moments it looked as if this first launch were to end in disaster.Fortunately, Mr. Charles Rolfe, who was in command of the capstan, had the presence of mind to shout to the spectators to seize hold and check the progress of the tube. A crowd of men, women, and children flung themselves upon the rope. There ensued a tug-of-war in which human muscles bested the pull of the tide, and the tube was brought up safely with its ends over the recesses cut in the towers. As the tide sank the ironwork came to rest in the exact position required by its designer. So accurately had all calculations been made that, though the tube was 460 feet long, there remained between the ends of the iron plates and the walls of the recesses a space somewhat less than an inch!
Raising the Tube
The first act of the play was finished. Little time was lost in proceeding with the second. The chains of the hydraulic presses were made fast to the lifting cradles attached to the tube ends. The steam-engines perched on the towers began to force water at enormous pressure into the cylinders of the presses; the rams emerged slowly. As the tube ascended, the masonry was built in underneath it, so that there should never be a clear space of more than a few inches under the ironwork. Robert Stephenson had insisted beforehand that, though the strength of the beams supporting the presses, and of the chains, was sufficient to bear the load, no risks were to be taken.
A Serious Disaster averted
The ends of the tube were lifted alternately, and they rose gradually to a height of about 30 feet. Then occurred an accident which proved only too conclusively how justifiable was Stephenson’s caution. Without the least warning, one of the hydraulic presses burst, and the tube fell 7 inches on to the packings which had been built up underneath it. So small a fall may appear to the uninitiated to be of slight consequence; but the momentum acquired by the 900 tons of iron grew, even in that small distance, to such proportions as to crumple up solid castings, weighing tons, as if they had been mere biscuit boxes. “Thank God,” wrote Mr. Clark, the engineer in charge, to Stephenson, “that you have been so obstinate; for if this accident had occurred with no bed for the end of the tube to fall on, it would have now been lying across the bottom of the straits.” As it was, this accident strained the tube, though fortunately not to a serious extent, and added an item of £5,000 to the cost – £234,450-of building the bridge.
A new cylinder having been provided, the tube was raised to its final position; and in due course its three gigantic brothers, each of which, if stood on end in St. Paul’s Churchyard, would tower 100 feet above the great cross, were set in their respective places.
All the Tubes raised
Alt four tubes for each track of rails were then joined together to form a continuous girder, 1,511 feet long, and weighing 5,000 odd tons, attached firmly to the Britannia Tower, but resting upon rollers on the two land piers and the abutments, to allow for expansion and contraction of the metal.
Testing the Bridge
On March 5, 1850, the now completed bridge was subjected to severe tests. First, three locomotives, coupled together, were moved across; then a train of twenty-four loaded coal wagons; and finally a heavy testing train of several hundred tons crossed at a speed of 35 miles an hour. The deflection caused by the load was less than half an inch, or barely one twenty-fifth of that to which the bridge might be subjected without danger. As Stephenson had designed the bridge to stand eight times the maximum load that could possibly be put upon it by an ordinary train, the slightness of the deflection was anticipated. Though the weight of locomotives and other rolling stock has increased greatly during the last half century, and nearly sixty years have passed since the opening of the bridge, there has been no talk of replacing Stephenson’s great structure by one of more modern design.
An Appreciation of the Bridge
“The Britannia Bridge,” wrote Dr. Smiles, “is one of the most remarkable monuments of the enterprise and skill of the present [nineteenth] century. Robert Stephenson was the master spirit of the undertaking. To him belongs the merit of first seizing the ideal conception of the structure best adapted to meet the necessities of the case, and of selecting the best men to work out his idea; himself watching, controlling, and testing every result by independent check and counter-check.
“But for the perfeetion of our tools, and the ability of our mechanics to use them to the greatest advantage; but for the matured powers of the steam-engine; but for the improvements in the iron manufacture, which enabled blooms to be puddled of sizes before deemed impracticable, and plates and bars of immense size to be rolled and forged,-but for these, the Britannia Bridge would have been designed in vain. Thus it was not the product of the genius of the railway engineer alone, but of the collective mechanical genius of the English nation.”
San Francisco’s Golden Gate Bridge
Written by Scott Messmore
The Golden Gate bridge is simply a technological marvel.
It took nearly ten years to build and even though the bridge builders set records for safety, men died creating the orange goliath. On one day alone, February 17, 1937, 10 men fell to their deaths when a scaffold broke off of the bridge and plunged through the safety net. A special group of men called the ‘half-way-to-hell club” had been saved by a net hung underneath the bridge. Nineteen men fell into the new innovation for worker safety. Standing 220 feet off of the water, the Gate is used by 41 million drivers and passengers each year. Since it opened to traffic in 1937, roughly 1.6 billion people have used the 1.7 mile long span. The highest point of the bridge is 746 feet and some of the foundations are 110 feet under water.
San Franciscan’s Approve $30Million During the GreatDepression
The idea to cross the Golden Gate strait was originated as early as 1872 by a railroad magnate. Not until 1916 was a serious attempt made to make the crossing. Bridge designer Joseph Strauss felt he could cross the Gate with a huge suspension bridge and do it for under $30 million dollars. In 1921, Strauss finalized a plan and set out to convince San Francisco citizens and leaders that it could, and should, be done.
Legislature and War Department Approve Plan forGolden Gate
The California Legislature formed the Golden Gate Bridge and Highway District in 1923 which allowed the bridge builders to borrow money, issue bonds and collect tolls from travelers. The future of the bridge was actually in the hands of the U.S. War Department in Washington D.C. The War Department had full control of all strategic ports and waterways in the United States. It owned the land on both sides of the Golden Gate and needed to know if a bridge would hinder marine navigation and if money was available for the project. The War Department agreed to the plan in 1924, but many San Franciscans were opposed to the bridge idea. Ferry companies that made their livelihoods carrying passengers across the strait mounted a stiff campaign to block the bridge. Bridge proponents eventually carried the day and Strauss was chosen as chief engineer in late 1929. A year later, voters living inside the Golden Gate Bridge District actually put their homes and businesses up for collateral to finance the project. It would be a $35 million dollar construction project. A remarkable endeavor in the depths of the Great Depression. The bridge was finished in 1937.
Three-dollar Fare to Cross theGolden Gate Bridge
Millions of visitors come to thebridge each year. The speedlimit of the bridge is now only45 miles per hour and tragic fines have been doubled for the bridge. A $3 fee is collected for southbound traffic and touristswho want to ride their bikesacross the bridge can take advantage of the 10-foot wide sidewalks.
This all changed in 1879 when construction began on a railway suspension bridge. This was designed by Thomas Bouch, builder of the Tay Railway Bridge that had opened the previous year. The collapse of the Tay Bridge with large loss of life on 28 December 1879 brought a halt to work on Bouch’s Forth Bridge with just part of one pier built.
The completely redesigned bridge that was started in 1883 remains one of the world’s most distinctive structures. It was opened by Edward, Prince of Wales on 4 March 1890. The bridge was constructed by Tancred-Arrol to a design by civil engineers Sir John Fowler and Benjamin Baker. In the aftermath of the Tay Bridge disaster the bridge was a testament to robust and conservative over-engineering.
The end result is a massive and remarkably imposing structure. It was built as three separate double cantilevers. When each had been constructed, they were linked together by 350ft long girder spans joined to the main structure of the bridge by huge pins. The whole bridge is balanced by 1000 ton c6uriterweights on the outside of the outer cantilever structures.
The Forth Rail Bridge has an overall length of over 8,000ft. The towers reach a height of 361ft and trains cross the river at a height of 158ft. The total cost came to £3.2m, 6ou~ting £250,000 for the abortive construction work on the earlier bridge. Construction involved the use of over 54,000 tons of steel and 6.5 million rivets.
During the seven years of construction, 4,000 men were employed, of whom 57 were killed in accidents. 8 more men were saved by safety boats positioned in the river under the working areas.
Although it was formally opened in 4 March 1890, the bridge was first used some weeks earlier, on 21 January. On that day two 1000ft long test trains each comprising a locomotive and 50 wagons, and each weighing 900 tons, rolled onto the bridge side by side from the south.
The bridge easily survived the test: though following the Tay disaster it is interesting to wonder about the feelings of the drivers of those first trains as they looked down at the river 150 feet below them. The bridge has been put to good use ever since. In 1907, 30,000 trains weighing a total of 14.5 million tons crossed the bridge. In contrast, in 2000, some 60,000 trains weighing a total of 10.5 million tons crossed the bridge.
When it was first constructed, the Forth Rail Bridge was regarded as the eighth wonder of the world. Familiarity breeds contempt, and it is easy to forget that this is a structure every bit as spectacular and remarkable as the Eiffel Tower, of which it can seem oddly reminiscent. The bridge can be viewed to really good effect from both North and South Queensferry: and the view from one of the many trains crossing it is equally worthwhile, especially of North and South Queensferry and of the Forth Road Bridge only a short distance to the west.